Electrolytic On-Site Generator

ABSTRACT

Method and apparatus for a low maintenance, high reliability on-site electrolytic generator incorporating automatic cell monitoring for contaminant film buildup, as well as automatically removing or cleaning the contaminant film. This method and apparatus preferably does not require human intervention to clean. For high current density cells, cleaning is preferably performed by reversing the polarity of the electrodes and applying a lower current density to the electrodes, preferably by adjusting the salinity or brine concentration of the electrolyte while keeping the voltage constant. Electrolyte flow preferably comprises water and brine flows which are preferably separately monitored and automatically adjusted. For bipolar cells, flow between modules arranged in parallel is preferably approximately equally distributed between modules and between intermediate electrodes within each module.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of now-allowed U.S. patentapplication Ser. No. 15/064,385, entitled “Electrolytic On-SiteGenerator”, filed Mar. 8, 2016, which is a divisional application ofU.S. patent application Ser. No. 14/154,579, entitled “ElectrolyticOn-Site Generator”, filed on Jan. 14, 2014, which application is adivisional application of U.S. patent application Ser. No. 13/198,276,entitled “Electrolytic On-Site Generator”, filed on Aug. 4, 2011, whichapplication claims priority to and the benefit of filing of U.S.Provisional Patent Application Ser. No. 61/371,585, entitled “LowMaintenance Electrolytic On-Site Generator,” filed on Aug. 6, 2010 andU.S. Provisional Patent Application Ser. No. 61/371,490, entitled“Reverse Polarity Cleaning and Electronic Flow Control Systems for LowIntervention Electrolytic Chemical Generators,” filed on Aug. 6, 2010;which application is also a continuation-in-part application of U.S.patent application Ser. No. 12/473,744, entitled “Reverse PolarityCleaning and Electronic Flow Control Systems for Low InterventionElectrolytic Chemical Generators”, filed on May 28, 2009, whichapplication claims priority to and the benefit of filing of U.S.Provisional Patent Application Ser. No. 61/056,718, entitled “ReversePolarity Cleaning for High Current Density Electrolytic Cells,” filed onMay 28, 2008, and which application is a continuation-in-partapplication of U.S. patent application Ser. No. 11/946,772, entitled“Low Maintenance On-Site Generator”, filed on Nov. 28, 2007 (whichissued as U.S. Pat. No. 7,922,890 on Apr. 12, 2011), which applicationclaims priority to and the benefit of filing of U.S. Provisional PatentApplication Ser. No. 60/867,557, entitled “Low Maintenance On-SiteGenerator”, filed on Nov. 28, 2006. All of the foregoing applicationsare incorporated herein by reference in their entireties for any and allpurposes.

TECHNICAL FIELD

The present invention relates to an electrolytic on-site generator whichis nearly free of maintenance.

BACKGROUND

Note that the following discussion refers to a number of publicationsand references. Discussion of such publications herein is given for morecomplete background of the scientific principles and is not to beconstrued as an admission that such publications are prior art forpatentability determination purposes.

Electrolytic technologies utilizing dimensionally stable anodes havebeen developed to produce mixed-oxidants and sodium hypochloritesolutions from a sodium chloride brine solution. Dimensionally stableanodes are described in U.S. Pat. No. 3,234,110 to Beer, entitled“Electrode and Method of Making Same,” wherein a noble metal coating isapplied over a titanium substrate. Electrolytic cells have had wide usefor the production of chlorine and mixed oxidants for the disinfectionof water. Some of the simplest electrolytic cells are described in U.S.Pat. No. 4,761,208, entitled “Electrolytic Method and Cell forSterilizing Water”, and U.S. Pat. No. 5,316,740, entitled “ElectrolyticCell for Generating Sterilizing Solutions Having Increased OzoneContent.”

Electrolytic cells come in two varieties. The first category comprisesdivided cells that utilize membranes to maintain complete separation ofthe anode and cathode products in the cells. The second categorycomprises undivided cells that do not utilize membranes, but that alsodo not suffer nearly as much from issues associated with membranefouling. However, it is well accepted that one of the major failuremechanisms of undivided electrolytic cells is the buildup of unwantedfilms on the surfaces of the electrodes. The source of thesecontaminants is typically either from the feed water to the on-sitegeneration process or contaminants in the salt that is used to producethe brine solution feeding the system. Typically these unwanted filmsconsist of manganese, calcium carbonate, or other unwanted substances.If buildup of these films is not controlled or they are not removed on afairly regular basis, the electrolytic cells will lose operatingefficiency and will eventually catastrophically fail (due to localizedhigh current density, electrical arcing or some other event). Typically,manufacturers protect against this type of buildup by incorporating awater softener on the feed water to the system to prevent thesecontaminants from ever entering the electrolytic cell. However, thesecontaminants will enter the process over time from contaminants in thesalt used to make the brine. High quality salt is typically specified tominimize the incidence of cell cleaning operations. Processes are wellknown in the art for purifying salt to specification levels that willavoid contaminants from entering the cell. However, these salt cleaningprocesses, although mandatory for effective operation of divided cells,are considered too complicated for smaller on-site generation processesthat utilize undivided cells.

U.S. patent application Ser. No. 11/287,531, which is incorporatedherein by reference, is directed to a carbonate detector and describesone possible means of monitoring an electrolytic cell for internal filmbuildup. Other possible means for monitoring carbonate buildup in cellsthat utilize constant current control schemes is by monitoring the rateof brine flow to the cell. As brine flow increases, it is usually, butnot always, indicative of carbonate formation on the cathode electrodewhich creates electrical resistance in the cell. Other than thesemethods and/or visual inspection of the internal workings of a cell,there currently is not an adequate method of monitoring the internalstatus of the buildup on an electrolytic cell.

The current accepted method of cleaning an electrolytic cell is to flushit with an acid (often muriatic or hydrochloric acid) to remove anydeposits which have formed. Typically, manufacturers recommendperforming this action on a regular basis, at least yearly, butsometimes as often as on a monthly basis. Thus there is a need for amore reliable method for insuring cleanliness of the electrolytic cellis to perform a cleaning process on an automated basis that does notrequire the use of a separate supply of consumables such as muriatic orhydrochloric acid, and that does not require operator intervention.

U.S. Pat. No. 5,853,562 to Eki, et al. entitled “Method and Apparatusfor Electrolyzing Water” describes a process for reversing polarity onthe electrodes in a membraneless electrolytic cell for the purpose ofremoving carbonate scale and extending the life of the electrolyticcell. This method of electrolytic cell cleaning is routinely used inflow through electrolytic chlorinators that convert sodium chloride saltin swimming pool water to chlorine via electrolysis. However, currentlyused flow through electrolytic cells are constructed of electrodes(anode and cathode) that both have common catalytic coatings. Aselectrical polarity is changed, the old cathode becomes the anode, andthe anode becomes the cathode. Special catalytic coatings have beendeveloped for these applications, For instance, Eltech Corporation hasdeveloped the EC-600 coating specifically for the swimming poolchlorination market. Sodium chloride is typically added to the poolwater raising the total dissolved solids (TDS) content to approximately4 to 5 grams per liter. At these TDS values, the current density in theswimming pool electrolytic cells is relatively low. The special anodecoatings for pool applications are designed to tolerate these lowcurrent densities for extended periods with polarity applied in eitherdirection. However, most dimensionally stable anodes for chlorineproduction in membraneless electrolytic cells producing chlorine at 8gram per liter (8,000 mg/L) concentration of free available chlorine(FAC) cannot tolerate high current densities (greater than approximately1 amp per square inch) in reverse polarity mode. Thus, although simplyreversing the polarity works for low current density electrolytic cells,it will not work for electrolytic cells which normally operate at a highcurrent density, since the anode will be damaged if high current densityis applied during the reverse polarity cleaning operation.

One of the other maintenance items for electrolytic generators is therequirement that operators occasionally measure and set water flow intothe system. The flow through the generator can vary greatly withincoming and outgoing water pressure and/or contaminant buildup in thesystem or electrolytic cells. Typically, measurements are made witheither flowmeters or with timed volume measurements, and adjustments tothe flow are performed with manual valves. Keeping the electrolyticgenerator operating within flow specifications is important, as itensures reliable long term operation the generator within its efficiencyspecifications.

SUMMARY

Embodiments of the present invention are related to a method foroperating an electrolytic cell, the method comprising the steps ofsupplying brine to an electrolytic cell, producing one or more oxidantsin the electrolytic cell, detecting a level of contaminant buildup,automatically stopping the brine supply after an upper contaminantthreshold is detected, automatically cleaning the electrolytic cell,thereby reducing contaminants in the electrolytic cell, andautomatically continuing to produce the one or more oxidants after alower contaminant threshold is detected. The cleaning step preferablycomprises providing brine to an acid generating electrolytic cell,generating an acid in the acid generating electrolytic cell, andintroducing the acid into the electrolytic cell. The acid preferablycomprises muriatic acid or hydrochloric acid. The method preferablyfurther comprises the step of diluting the brine. The detecting steppreferably comprises utilizing a carbonate detector. The detecting steppreferably comprises measuring the rate of brine consumption in theelectrolytic cell, optionally by measuring a quantity selected from thegroup consisting of flow meter output, temperature of the electrolyticcell, brine pump velocity, and incoming water flow rate. The methodpreferably further comprises comparing the rate of brine consumption tothe rate of brine consumption in a clean electrolytic cell. The cleaningstep optionally comprises using an ultrasonic device and/or using amagnetically actuated mechanical electrode cleaning device, or reversingthe polarity of electrodes in the electrolytic cell, thereby loweringthe pH at a cathode.

Embodiments of the present invention also are related to an apparatusfor producing an oxidant, the apparatus comprising a brine supply, anelectrolytic cell, an acid supply, and a control system forautomatically introducing acid from the acid supply into theelectrolytic cell. The acid supply preferably comprises a secondelectrolytic cell, and the brine supply preferably provides brine to thesecond electrolytic cell during a cleaning cycle. The apparatuspreferably further comprises a variable speed brine pump, a carbonatedetector, one or more thermowells for measuring a temperature of saidelectrolytic cell, and/or one or more flowmeters for measuring the brineflow rate.

Embodiments of the present invention also are related to an apparatusfor producing an oxidant, the apparatus comprising a brine supply, anelectrolytic cell, a cleaning mechanism in the electrolytic cell, and acontrol system for automatically activating the cleaning mechanism. Thecleaning mechanism preferably is selected from the group consisting ofultrasonic horn, magnetically actuated electrode mechanical cleaningdevice, and acidic solution at a cathode surface. The apparatuspreferably further comprises a device selected from the group consistingof a carbonate detector, at least one thermowell for measuring atemperature of said electrolytic cell, and a flowmeter for measuring abrine flow rate.

Embodiments of the present invention also are related to a method forcleaning an electrolytic cell comprising electrodes, the methodcomprising the steps of reversing polarities of two or more of theelectrodes and providing a cleaning current density to the electrodeswhich is lower than an operational current density used during normaloperation of the electrolytic cell. During normal operation theelectrolytic cell preferably produces a concentration of free availablechlorine greater than approximately four grams per liter, morepreferably greater than approximately five grams per liter, and mostpreferably approximately eight grams per liter. The operational currentdensity is preferably greater than approximately one amp per squareinch. The cleaning current density is preferably less than approximately20% of the operational current density, and more preferably betweenapproximately 10% and approximately 15% of the operational currentdensity. The providing step is preferably performed for less thanapproximately thirty minutes, and more preferably for betweenapproximately five minutes and approximately ten minutes. The reversingstep optionally comprises using at least one power supply relay or otherswitching device. The operational current density is preferably providedby an operational power supply and the cleaning current density ispreferably provided by a separate cleaning power supply. The powerproducing capacity of the cleaning power supply is preferably smallerthan the power producing capacity of the operational power supply. Themethod preferably further comprises the step of monitoring a flow rateof electrolyte through the electrolytic cell. The monitoring step ispreferably performed using a flowmeter, a rotameter, or a pressuretransducer, or monitoring a temperature difference across theelectrolytic cell via a first thermocouple or thermowell disposed at aninlet of the electrolytic cell a second thermocouple or thermowelldisposed at an outlet of the electrolytic cell. The method preferablyfurther comprises the step of automatically adjusting the flow rate, andpreferably further comprises the step of initiating a cleaning cycle ata predetermined flow rate.

Embodiments of the present invention also are related to a method forcleaning an electrolytic cell comprising electrodes, the methodcomprising the steps of reversing polarities of two or more of theelectrodes and providing a cleaning voltage potential difference to theelectrodes which is lower than an operational voltage potentialdifference used during normal operation of the electrolytic cell. Duringnormal operation the electrolytic cell preferably produces aconcentration of free available chlorine greater than approximately fivegrams per liter. The providing step is preferably performed for a timebetween approximately five minutes and approximately ten minutes. Thereversing step preferably comprises using at least one power supplyrelay or other switching device. The operational voltage potentialdifference is preferably provided by an operational power supply and thecleaning voltage potential difference is preferably provided by aseparate cleaning power supply. The method preferably further comprisesthe steps of monitoring a flow rate of electrolyte through theelectrolytic cell and automatically adjusting the flow rate.

Embodiments of the present invention also are related to an apparatusfor producing electrolytic products, the apparatus comprising anelectrolytic cell comprising electrodes; a first power supply forproviding a first current density to the electrodes, a second powersupply for providing a second current density to the electrodes, thesecond power supply having an opposite polarity to the first powersupply, wherein the second current density is smaller than the firstcurrent density. The electrolytic cell preferably produces aconcentration of free available chlorine greater than approximately fivegrams per liter. The second current density is preferably betweenapproximately 10% and approximately 15% of the first current density.The apparatus preferably further comprises at least one power supplyrelay or other switching device, and preferably comprises a flowmonitoring device for monitoring a flow rate of electrolyte through theelectrolytic cell. The flow monitoring device is preferably selectedfrom the group consisting of a flowmeter, a rotameter, a pressuretransducer, a pair of thermocouples, and a pair of thermowells. If apair of thermocouples or thermowells is used, one thermocouple orthermowell is preferably disposed at an inlet of the electrolytic celland another thermocouple or thermowell is preferably disposed at anoutlet of the electrolytic cell. The apparatus preferably furthercomprises an electronically operated valve for adjusting the flow rate.

An embodiment of the present invention is a method for operating anelectrolytic cell, the method comprising monitoring a brine flow rate,monitoring a water flow rate and pressure, forming an electrolyte bymixing brine and water, automatically and separately adjusting the brineflow rate and the water flow rate so that a pressure and flow rate ofthe electrolyte are within predetermined limits prior to electrolysis ofthe electrolyte, and electrolyzing the electrolyte. Automatically andseparately adjusting the brine flow rate and the water flow ratepreferably ensures that a salinity and/or concentration of theelectrolyte are within predetermined limits prior to electrolysis of theelectrolyte. The method preferably further comprises monitoring anelectrolyte temperature and/or an oxidant temperature. The methodpreferably further comprises reducing the pressure of the water to anelectrolysis operating pressure. The method preferably further comprisesstopping electrolysis to avoid damage caused by incoming water pressurebeing too high or too low. Automatically and separately adjusting thebrine flow rate and the water flow rate is preferably performed inresponse to an electrolyte temperature, an oxidant temperature, anelectrolysis current density, a water flow rate, a water pressure, abrine flow rate, or combinations thereof. The method preferably furthercomprises selecting a low threshold amount of oxidant in an oxidant tankwhich signals initiation of electrolysis and initiating electrolysis ofthe electrolyte when electricity costs are low even though an oxidantamount in the oxidant tank is higher than the low threshold amount.

An embodiment of the present invention is an apparatus for performingelectrolysis, the apparatus comprising a brine input line comprising avariable speed brine pump and an on-off switch, a water input linecomprising a pressure sensor, a flow meter, and a flow control valve, aconnection between the brine input line and the water input line, anelectrolytic cell, and an oxidant tank. The apparatus preferably furthercomprises a pressure reducing valve on the water input line a checkvalve on the brine input line, a temperature measuring device formeasuring an electrolyte temperature, and/or a temperature measuringdevice for measuring an oxidant temperature. The apparatus preferablyfurther comprises a controller for separately controlling operation ofthe variable speed brine pump and the water flow control valve. Thecontroller preferably operates in response to one or more inputsselected from the group consisting of an electrolyte temperature, anoxidant temperature, a current density in the electrolytic cell, a waterflow rate, a water pressure, and a brine flow rate.

An embodiment of the present invention is a method of cleaning anelectrolytic cell, the method comprising lowering a salinity of anelectrolyte until a current density of the electrolytic cell falls to orbelow a predetermined cleaning current density, reversing a electrodepolarity, maintaining a constant electrode voltage, ceasing a flow ofwater into the electrolytic cell, operating the electrolytic cell untilthe current density increases to or above the predetermined cleaningcurrent density, starting the flow of water into the electrolytic celluntil the current density decreases to or below the predeterminedcurrent density, and repeating the ceasing, operating, and startingsteps. Repeating the ceasing, operating, and starting steps preferablyphysically dislodges contaminants from the cell. A flow of brine intothe electrolytic cell and a flow of water into the electrolytic cell arepreferably independently controllable. The lowering step preferablycomprises stopping the flow of brine. The method optionally furthercomprises increasing a salinity of electrolyte if the current densitydoes not increase sufficiently during the operating step. The method ispreferably performed when an amount of oxidant in an oxidant tank is ator below a predetermined low threshold amount and after the occurrenceof a predetermined event selected from the group consisting of a timeperiod elapsing, exceeding an operation time of the cell, exceeding anamount of electrolyte flow through the cell, and reaching acontamination level. The method preferably further comprises initiatingnormal operation of the electrolytic cell substantially immediatelyafter cleaning is complete and flushing debris such as scale flakes fromthe electrolytic cell once cleaning is complete. The method ispreferably performed in approximately three to five minutes. Therepeating step is preferably performed approximately every thirtyseconds. The method is preferably performed approximately once permonth. The predetermined cleaning current density and the total cleaningtime are preferably chosen to expose the electrolytic cell to apredetermined amount of amp-seconds, such as 1800 amp-seconds.

An embodiment of the present invention is a bipolar electrolytic cellcomprising a plurality of modules arranged in parallel, each modulecomprising primary electrodes and one or more intermediate electrodes; amanifold for distributing electrolyte substantially evenly between eachmodule; a flow diffuser in each module located inside an electrolyteinlet; and a gap region in each module or openings in one or more of theintermediate electrodes to facilitate uniformity of electrolyte andoxidant flow in the electrolytic cell; wherein a general flow directionof electrolyte in each module is parallel to the electrodes. The flowdiffuser preferably blocks electrolyte entering each module from flowingdirectly between the electrodes. The gap region is optionally formed bythe shape of the intermediate electrodes or by the size of an edgeprotector. The edge protector preferably comprises one or more groovesfor receiving and holding the intermediate electrodes and preferablycomprises chlorinated polyvinyl chloride (CPVC) or Viton®. The edgeprotector is preferably replaceable by a different size edge protector,thereby enabling a single module housing to accommodate different sizesof intermediate electrodes. The openings on an intermediate electrodeare preferably staggered or offset from openings in adjacentintermediate electrodes.

An embodiment of the present invention is also a method of operating abipolar electrolytic cell, the method comprising substantially evenlydistributing a flow of electrolyte entering the electrolytic cellbetween a plurality of modules whose inlets and outlets are connected inparallel, diffusing a flow of electrolyte entering each module so thatelectrolyte flow is substantially even between one or more intermediateelectrodes present in each module, mixing the electrolyte flows betweenthe intermediate electrodes in a gap region or via openings in one ormore of the intermediate electrodes, and generally flowing electrolytein a direction parallel to the intermediate electrodes. The diffusingstep preferably comprises blocking electrolyte entering each module fromflowing directly between the intermediate electrodes. The methodpreferably further comprises selecting a low threshold amount of oxidantin an oxidant tank which signals initiation of electrolysis, andinitiating electrolysis of the electrolyte when electricity costs arelow even though an oxidant amount in the oxidant tank is higher than thelow threshold amount.

Objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate embodiments of the present inventionand, together with the description, serve to explain the principles ofthe invention. The drawings are only for the purpose of illustratingcertain embodiments of the invention and are not to be construed aslimiting the invention. In the drawings:

FIG. 1 is a diagram of one embodiment of a low maintenance on-sitegenerator unit.

FIG. 2 is a schematic of a reverse polarity system for electrolytic cellcleaning.

FIG. 3 is a diagram of an embodiment of an on-site generator inaccordance with the present invention.

FIG. 4 is an isometric view of an embodiment of a cell of the presentinvention, for example for use with the on-site generator of FIG. 3.

FIG. 5A is a cutaway end view of the inlet side of a module of the cellof FIG. 4.

FIG. 5B is a perspective view of the outlet side of a module of the cellof FIG. 4.

FIG. 6 is a cross section view of an alternative module.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present invention are methods and devices whereby anon-site generator electrolytic cell is preferably monitoredautomatically for buildup of contaminants on the electrode surfaces, andwhen those contaminants are detected, the electrolytic cell is cleanedautomatically (i.e, without operator intervention), thereby providing asimple, low cost, and reliable process for achieving a highly reliable,low maintenance, on-site generator which does not require the typicaloperator intervention and/or auxiliary equipment (such as a watersoftener) now required for long life of electrolytic cells.

The internal status of the electrolytic cells can be monitoredautomatically by monitoring cell inputs and performance. It is knownthat how much brine a cell consumes is dependent on the amount and typeof film buildup on that given cell. If brine flow is continuouslymonitored, any dramatic change in brine flow to reach a given current ata given voltage is indicative of a potential problem with film buildupwithin a cell. The invention preferably monitors the flowcharacteristics of the brine, incoming water, temperature, etc., todetermine whether or not there has been contaminant buildup within theelectrolytic cell. When potential film buildup is detected in the cellby the control system, the cell is preferably automatically acid washed.

A carbonate detector integrated with an electrolytic cell, automaticacid washing, and device controls may be utilized. A separateelectrolytic cell from the one used to create the mixed oxidant orsodium hypochlorite is preferably used to create the acid on site and ondemand and to provide the acid for removing of contaminants in theelectrolytic cell used for creating the sodium hypochlorite or mixedoxidants. Alternatively a reservoir is used to store concentrated acidonsite for cleaning the cell, and monitoring that acid reservoir andalarming operators when that acid reservoir would need to be refilled,as well as optionally diluting the acid to a desired concentration priorto washing the cell. An ultrasonic cleaning methodology forautomatically removing unwanted contaminants when the contaminants aredetected by the methods described above may also be integrated into thepresent invention.

An embodiment of the present invention is shown in FIG. 1. All of thecomponents of this device are preferably mounted to back plate 15. Thecontrols and power supplies for all the separate components shown inthis embodiment are all preferably contained within control box 5, butmay alternatively be located wherever it is convenient, preferably aslong as there are master controls for the overall operation of theapparatus.

Control box 5 preferably shows the status of the unit via display 10,and the master controls as well as electrical power and/or componentsignals are preferably carried via electrical connections 50 betweencontrol box 5 and the various individual components. Water (preferablysoft water) preferably enters the system through water entrance pipe 30,and brine preferably enters the system through brine entrance pipe 25.Brine, preferably stored in a saturated brine silo or tank, ispreferably pumped via variable speed brine pump 20, which is preferablycontrolled and powered by electrical connection 50. The brine thenpreferably passes through flow meter 35, which can be electricallymonitored via electrical connection 50. The control system can controlthe flow rate of the brine by increasing the speed of variable speedbrine pump 20.

When the electrolytic generator is in normal operation mode and is attarget current and target voltages, the total flow through theelectrolytic cell 55 can be monitored, for example by a flowmeter,rotameter, or pressure transducer, or by monitoring the change intemperature across the electrolytic cell 55 by monitoring inletthermowell 65 and exit thermowell 70. When control box 5 determines thatflow is off target, for example in response to fluctuations in incomingpressure and/or flow to the electrolytic generator, it preferablyautomatically adjusts flow by changing electronically controlled cellinlet valve 6. In this way, the cell can always operate near target flowlevels and will not routinely require measurement or adjustment ofincoming flows.

Data from any of the following sources (or combinations of data from anyof these sources) is preferably used to determine the volumetric flowrate of brine: flow meter 35, carbonate detector 60, electrolytic cell55, acid generating electrolytic cell 45, and/or thermowells 65, 70.Valve 40 can direct flow either to electrolytic cell 55 or to acidgenerating electrolytic cell 45. Valve 40 typically flows an electrolytecomprising diluted brine (as both the concentrated brine and waterinflows have preferably been plumbed together and the brine has beendiluted before it reaches valve 40) to electrolytic cell 55. In thisstandard operating configuration, the system produces, for example,mixed oxidants or sodium hypochlorite.

As contaminants build up on carbonate detector 60, which may be locatedelsewhere according to the present invention, carbonate detector 60sends a series of signals to control box 5, preferably via electricalconnections 50, which indicate whether or not a contaminant film isbuilding up on electrolytic cell 55. When carbonate detector 60indicates that there is contaminant film, control box 5 preferablybegins an acid cleaning cycle in the device, wherein valve 40 isactuated via electrical connection 50 to force diluted brine throughacid generating cell 45, which is also preferably energized by controlbox 5 via electrical connections 50. The system preferably runs brinepump 20 to flow at a rate (as measured by flow meters 35) which has beenoptimized for optimal acid creation in acid generating electrolytic cell45. In this embodiment, the acid created in acid generation cell 45preferably flows through electrolytic cell 55, where it preferablycleans the contaminants, then flows through carbonate detector 60. Thesystem preferably runs in this acid cleaning mode until carbonatedetector 60 sends a signal to control box 5 indicating that the systemis clean and can begin running again in standard mixed oxidant or sodiumhypochlorite production mode. The acid used to clean electrolytic cell55 is preferably dumped to a separate waste drain after flowing throughcarbonate detector 60 instead of dumping it to the oxidant storage tank.Electrolytic cell 55 may optionally be cleaned with an ultrasonic hornand/or a magnetically actuated electrode mechanical cleaning apparatusin addition to or in place of using an acid generating cell.

In an alternative embodiment, concentrated acid is stored in areservoir. During the acid cleaning cycle, control box 5 preferablyactivates a pump or valve to allow flow of the acid to electrolytic cell55. The reservoir is preferably large enough to accommodate manydifferent acid wash cycles. Some of that acid may potentially be dilutedwith standard incoming water to clean electrolytic cell 55.

If carbonate detector 60 (or any other contaminant detecting component)is not used, electrolytic cell 55 preferably may be cleaned on apredetermined cleaning schedule to ensure contaminants do not ruinelectrolytic cell 55. Typically this cleaning schedule would be basedupon the number of hours that the electrolytic cell had been runningsince the last cleaning was completed, and is preferably frequent enoughto ensure that there is no excessive contaminant buildup on theelectrolytic cell.

The rate of brine consumption may optionally be used to determine thepresence of contaminants in electrolytic cell 55. In normal operation ina clean cell, the rate of brine consumption is steady and measurable. Ascarbonate scale builds up within electrolytic cell 55, the carbonatelayer acts as an electrical insulator between the anode and cathodewithin electrolytic cell 55. To compensate for this insulating effect,and to maintain the amperage within electrolytic cell 55, the rate ofbrine consumption increases to increase the conductivity withinelectrolytic cell 55. This increased rate of brine consumption iscompared to the normal rate of brine consumption. Flow throughelectrolytic cell 55 can also be used to measure contaminant buildupwithin electrolytic cell 55. Flow can be measured indirectly bymeasuring the temperature rise through electrolytic cell 55, for exampleby comparing the temperature difference between two thermocouples orinlet thermowell 65 and cell discharge thermowell 70. When carbonatebuildup is detected by any of these means, electrolytic cell 55 can becleaned by any of the methods or components described above. Brineconsumption may be measured using brine flow rate, tachometer rates ofbrine pump 20, or incoming water flow rates.

In addition to (or instead of) the cleaning methods described above, theelectrolytic cell may optionally be cleaned by reversing the polarity ofthe electrodes in electrolytic cell, while flowing electrolyte throughthe electrolytic cell or not, and preferably for a very short duration.Reversing the polarity of the electrodes, preferably at low currentdensities, lowers the pH at the cathode, which dissolves and removes thecontaminants. However, the dimensionally stable anode in the chlorine (4to 8 gm/L) producing electrolytic cell described herein typicallyoperates well at high current densities (up to 2 amps per square inch),but would fail quickly if polarity were reversed at the same currentdensity. Thus it is preferable to use a separate power source at lowercurrent density and/or lower plate to plate voltages to clean the cellin reverse polarity mode, which is only operated when the normalchlorine production operational mode is in standby, so that the primaryanode coating remains undamaged. Under these conditions, cleaning cyclesof less than 30 minutes can be achieved, preferably ranging betweenapproximately 5 minutes and 10 minutes. Industry experience indicatesthat cell cleaning intervals of less than a week would represent anunfavorable situation where the feed water to the electrolytic cell, orthe salt used to make the brine solution, would typically be poorquality. Intervals between cleaning of greater than one week are clearlythe industry norm. Under the worst case condition of cleaning once perweek, the loss of system duty cycle (production operation mode) wouldstill be negligible.

In any embodiment using reverse polarity to clean the electrolytic cell,both the anode and cathode surfaces of both primary and bi-polarelectrodes are preferably coated with an appropriate dimensionallystable anode coating.

FIG. 2 is a schematic of an embodiment of a system for implementingreverse polarity cleaning. Electrolytic cell 130 comprises anode 134 andcathode 132 with electrolyte flowing in at the bottom and oxidantflowing out at the top of the cell. In normal operation, electrolyticcell 130 has electrical energy applied to anode 134 and cathode 132 viamain power supply 136. Periodically, electrolytic cell 130 will becleaned by reversing the polarity on anode 134 and cathode 132,effectively making anode 134 the cathode, and cathode 132 the anode. Inthe normal mode of production where the system is producing a chlorinebased disinfectant, the current density on anode 134 is preferablybetween approximately 1 and 2 amps per square inch. To avoid damage toanode 134 during the reverse polarity cleaning step, the current densityis preferably less than approximately twenty percent of the normaloperating current density range, and more preferably between about 10%and 15% of the normal operating current density range. Because thereverse polarity cleaning operation operates at much lower powersettings, power is preferably supplied by cleaning power supply 138,which can be much smaller than main power supply 136. Power from mainpower supply 136 is transferred to electrolytic cell 130 preferably viamain power cables 144. Power from cleaning power supply 138 istransferred to electrolytic cell 130 preferably via cleaning powercables 146. The power supplies are preferably isolated via main powersupply relay 140 and cleaning power supply relay 142. In normaloperation when chlorine is being produced within electrolytic cell 130,main power supply 136 is energized and main power supply relay 140 isclosed. To avoid backflow of current to cleaning power supply 138 withthe wrong polarity, cleaning power supply relay 142 is open. Likewise,when electrolytic cell 130 is operating in cleaning mode, cleaning powersupply 138 is energized, main power supply 136 is de-energized, mainpower supply relay 140 is open, and cleaning power supply relay 142 isclosed. By utilizing less current density and/or lower potentials onanode 134 during the short cleaning cycle, damage to anode 134 orcathode 132 due to the cleaning cycle is negligible.

An alternative embodiment to the one shown in FIG. 2 uses the main powersupply 136 to provide power for normal operation as well as the cleaningcycles. This approach preferably employs the use of power supply relays142 or other switching devices to reverse the polarity. Typically thisapproach requires the electrolytic cell brine concentrations during thecleaning cycle to be much less than in normal operation. With thisapproach, however, it is still preferable that the cleaning cycle beperformed at lower current densities and/or lower potentials for shortperiods of time.

FIG. 3 is an embodiment of an on-site generator of the presentinvention. Brine from storage tank 325 preferably passes through brinefilter 330, on-off solenoid 335, variable speed brine pump 340, andcheck valve 345 before it is mixed with water. Brine filter 330 ispreferably located outside the generator enclosure for easy access forfilter replacement. Solenoid 335 is used to stop brine flow duringcleaning, as described below, and also prevents over-pressure brine fromseeping into electrolytic cell 355. Check valve 345 prevents softenedwater from backflowing into the brine line. Flow 300 of water(preferably softened water) preferably passes through flow sensor 305,such as a rotameter, past pressure transducer 310, through flow controlvalve 315, and through before it is mixed with brine. Pressure reducingvalve 320 preferably reduces the pressure of the incoming water, whichmay be as high as 60 psi, to the pressure at which electrolytic cell 355operates, which is preferably approximately 5-6 psi. Pressure reducingvalve 320 also prevents the electrolytic cell from being subjected tohigh pressures, which may cause a rupture disk or other similar deviceto blow. The water/brine solution (electrolyte) preferably passesthrough inlet thermowell 350 before it enters electrolytic cell 355.After electrolysis the mixed oxidants preferably exit the cell throughoutlet thermowell 360 before being stored in oxidant storage tank 370.In this embodiment the water flow and brine flow rates are preferablyseparately and/or automatically controllable. By separately monitoringand preferably automatically controlling the water flow, a consistentflow rate can be provided to the electrolytic cell, even if the incomingwater pressure or flow rate fluctuates. In case of large fluctuations,this control enables a smooth shutdown of the system until the inletwater pressure is within specified limits again. This enables greatlyenhanced control of the electrolytic process. Dual processors, one forflow control and the other for controlling the cell power supply, may beemployed.

As described above, reverse polarity cleaning is preferably carried outat a lower current density than that used for normal cell operation.Typically this current density can be achieved by one or more of thefollowing: lowering the voltage, lowering the salinity of theelectrolyte (e.g. the brine concentration), and/or lowering theoperating temperature (since the resistivity of water rises as thetemperature decreases). An embodiment of the present inventionpreferably performs reverse polarity cleaning according to the followingprocedure:

1) Turn off the brine flow.

2) Flush the electrolytic cell preferably with soft water, preferablyfor approximately one to three minutes, thus reducing salinity andtemperature in the cell. The current typically spikes to a number higherthan the desired cleaning current density (the desired cleaning currentdensity may be, for example, 10 A, if the normal operating currentdensity is 75 A, or about 10%-15% of the normal operating currentdensity);

3) Continue to flow water through cell until the cell salinity andtemperature is low enough (i.e. the resistivity of the solution in thecell is high enough) so that the current falls below the desiredcleaning current density.

4) Turn off the water flow; the cell is now preferably substantiallyfilled with water.

5) Reverse the polarity of the power cell, preferably keeping thevoltage constant. Since the cell is operating, the cell temperaturetypically increases, thereby increasing the current due to the decreasedresistivity of the hotter water.

6) When the current reaches approximately the desired cleaning currentdensity, turn on the water flow again.

7) Repeat steps 3-6 approximately every 30 seconds or less for thedesired cleaning duration, for example approximately 3-5 minutes;

8) Flush debris from the cell for approximately 30 seconds, then proceedto normal operational startup.

In addition to keeping the desired cleaning current densityapproximately at or below a desired value, this throttling of the waterflow also has the physical effect of dislodging contaminants such asscale flakes from the cell. This procedure is enabled by use of anautomatic water flow control valve, such as a solenoid controlled valve,PWM valve, or 0-5V valve, which is controlled by the measured currentdensity. Water flow may be controlled by a PID(proportional-integralderivative) controller, which preferably uses flowrate, pressure, and/or temperature as control inputs.

If the current at turn on in step (2) doesn't spike above the desiredcleaning current density, or if the current doesn't reach that level instep (6), then brine may optionally be injected into the cell during thecleaning procedure in order to increase the current density to thedesired level. Then the procedure may be continued as described above.

The system preferably normally operates when the level of the oxidantstorage tank, which contains the output of the electrolytic cell, isbetween a preset low level and a preset high level. In other words, thesystem preferably automatically turns on when the tank is low and turnsoff when the tank is full. The cleaning procedure is preferablyinitiated when the system indicates that cleaning is required (forexample after a preset period of time or operation time, e.g. 720 hours,or preset amount of flow, or when contamination is measured and reachesa maximum desired level) AND when the oxidant tank has sufficientlyemptied to be at the preset low level. This ensures that normaloperation will resume immediately after the cleaning step, therebyflushing any contaminants or debris out of the cell (and into theoxidant tank, which is easily cleaned) before they have a chance tosettle. Furthermore, the cleaning operation preferably does notappreciably dilute the oxidant solution stored in the oxidant storagetank.

During the above reverse polarity cleaning procedure the cell issubjected to a certain amount of amp-seconds. For example, a threeminute cleaning period run at 10 A would result in a total of 1800A-sec. The time and current may alternatively be chosen to be atdifferent values which give approximately the same (or similar) A-secvalue. For example, a 30 second cleaning period may be run at 60 A, thusgiving the same total of 1800 A-sec. This may result in the samecleaning efficacy, but allows for shorter cleaning time periods, thuspotentially allowing for cleaning to be performed more frequently.However, care must be taken so that the higher reverse polarity cleaningcurrent density doesn't damage the anode. (Such higher current densityis still preferably less than or equal to the normal operational currentdensity.) A typical cleaning cycle may be run as infrequently as fiveminutes once a month.

FIG. 4 is a view of an embodiment of a bipolar cell of the presentinvention. The cell is preferably a horizontal flow cell. The cell showncomprises a plurality of modules 500, each preferably separated by aprimary electrode and sealed by an o-ring or similar seal. Each modulepreferably comprises one or more intermediate electrodes (not shown). Ascan be seen, flow of electrolyte into each module (via inlet manifold510), and oxidant out from each module (via outlet manifold 520), occursin parallel. Inlet manifold 510 preferably provides equal flow to allmodules in parallel. Not only is the flow through the cell preferablyparallel to each of the electrodes, but also the cells are preferablyarranged in parallel with one another with respect to the flow. Othercells known in the art are configured in series, so that theelectrolyte/oxidant flowing into one module comes from the output of theprevious module. The configuration of this embodiment allows for asingle defined footprint for the product, regardless of the number ofmodules used. In contrast, series systems require vastly differentfootprints depending on the number of modules used. In addition, becausethe electrolyte quality varies greatly from module to module in seriessystems, certain modules wear out faster must be replaced frequently, orthe modules must be rotated. In contrast, with a parallel system, theelectrolyte entering each module is exactly the same for each module.Thus the modules wear evenly. (Typically the entire cell is replacedwhen the modules eventually wear out.)

FIG. SA is a cutaway end view of the inlet end of one of the modules ofthe cell of FIG. 4. The module preferably comprises one or morepreferably parallel intermediate electrodes 530. In this figure, theflow direction of the electrolyte entering the module is into the page.The module preferably comprises flow diffuser 550 which blockselectrolyte from flowing directly into the cell, forcing it down into,for example, distribution area 570 and around flow diffuser 550, therebydistributing the electrolyte entering the module from inlet 540substantially evenly between all of the intermediate electrodes. Flowdiffuser 550 may be rigid or flexible, and may comprise a chemicallyresistant material such as chlorinated polyvinyl chloride (CPVC) orViton®.

FIG. SB is a perspective view of the outlet end of one of the modules ofthe cell of FIG. 4. Each intermediate electrode 530 is preferablyconfigured via extension 535 to form gap 600. Although gap 600 is shownat the bottom of intermediate electrode 530, it may alternatively belocated anywhere along the edge of intermediate electrode 530. More thanone gap may optionally be used. Gap 600 preferably facilitates mixing ofthe flows exiting the intermediate electrodes, thus helping to ensurethat there are equivalent flows between all of the intermediateelectrodes, and thereby improving cell efficiency. Alternatively, theelectrode may be rectangular and an edge protector may compriseextension 535, configured to form gap 600. The edge protector serves tohold the intermediate electrodes in the cell and preferably compriseschlorinated polyvinyl chloride (CPVC) and preferably comprises aplurality of grooves, each for receiving an intermediate electrode. Theedge protector and/or another edge protector along a different side ofthe electrodes may optionally comprise a compressible Viton® gasket,which has significant cost advantages. Using such a gasket on one edgeallows for cost reduction without significantly sacrificing rigidity.Any of the edge protectors is preferably replaceable by an edgeprotector having a different width. This enables the same cell enclosureto be used for different sized intermediate electrodes, which may beused in systems with different chemistries and/or electrode coatings.

FIG. 6 is a cross section of an alternative embodiment of anelectrolytic cell in accordance with the present invention comprisingprimary electrodes 610, 620, intermediate electrodes 630, and edgeprotectors 640, 650. Each intermediate electrode preferably comprisesone or more holes or openings 660. These openings preferably help tobalance the electrolyte flow throughout the electrolytic cell, resultingin better cell efficiency. The openings on each intermediate electrodeare preferably staggered or offset from the openings on the adjacentintermediate electrode(s), thus providing a tortuous path for electronssuch that the vast majority of electrons are forced to travel throughthe catalytic electrode coatings.

Power Saver Programming

During normal operation, if the oxidant storage tank is at apredetermined low level, the system preferably turns on and producesmore oxidant, and stops when the level reaches a predetermined highlevel. The system does not ordinarily turn on if the level of oxidant inthe oxidant tank is between the high and low levels. However, in orderto save electricity costs, before the oxidant level falls to the lowlevel (i.e. when the level of oxidant in the oxidant tank is between thehigh and low levels), embodiments of the present system may be turned onduring times when electricity costs are least expensive in order to “topoff” the tank, thus pre-empting later operation when electricity is moreexpensive and the oxidant level falls to the low level.

Although the invention has been described in detail with particularreference to the described embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverall such modifications and equivalents. The entire disclosures of allpatents and publications cited above are hereby incorporated byreference.

1. A bipolar electrolytic cell, comprising: a plurality of modulesarranged in parallel, each module comprising primary electrodes and oneor more intermediate electrodes; a manifold for distributing electrolytesubstantially evenly between each module; a flow diffuser in each modulelocated inside an electrolyte inlet; and a gap region in each module oropenings in one or more of the intermediate electrodes to facilitateuniformity of electrolyte and oxidant flow in the electrolytic cell;wherein a general flow direction of electrolyte in each module isparallel to the electrodes.
 2. The bipolar electrolytic cell of claim 1,wherein the flow diffuser blocks electrolyte entering each module fromflowing directly between the electrodes.
 3. The bipolar electrolyticcell of claim 1, wherein the gap region is formed by the shape of theintermediate electrodes.
 4. The bipolar electrolytic cell of claim 1,wherein the gap region is formed by the size of an edge protector. 5.The bipolar electrolytic cell of claim 4, wherein the edge protectorcomprises one or more grooves for receiving and holding the intermediateelectrodes.
 6. The bipolar electrolytic cell of claim 4 wherein the edgeprotector comprises chlorinated polyvinyl chloride (CPVC) or Viton®. 7.The bipolar electrolytic cell of claim 4, wherein the edge protector isreplaceable by a different size edge protector, thereby enabling asingle module housing to accommodate different sizes of intermediateelectrodes.
 8. The bipolar electrolytic cell of claim 1, wherein theopenings on an intermediate electrode are staggered or offset fromopenings in adjacent intermediate electrodes.
 9. A method of operating abipolar electrolytic cell, the method comprising: with a manifold,substantially evenly distributing a flow of electrolyte entering theelectrolytic cell between a plurality of modules arranged in parallel,each module comprising primary electrodes and one or more intermediateelectrodes, each module comprising an inlet and a flow diffuser locatedinside the inlet of the module, and each module being configured forelectrolyte flow generally parallel to the electrodes of the module;diffusing a flow of electrolyte entering each module with the flowdiffuser of the module such that the electrolyte flow is substantiallyeven between one or more intermediate electrodes present in each module;mixing the electrolyte flows between the intermediate electrodes in agap region of a module or one or through more openings present in one ormore of the intermediate electrodes; and flowing the electrolyte in adirection generally parallel to the intermediate electrodes.
 10. Themethod of claim 9, wherein the diffusing comprises blocking electrolyteentering each module from flowing directly between the intermediateelectrodes.
 11. The method of claim 9, further comprising: selecting alow threshold amount of oxidant in an oxidant tank, which amount signalsinitiation of electrolysis; and initiating electrolysis of theelectrolyte when an oxidant amount in the oxidant tank is higher thanthe low threshold amount.